Enhancement of the fracture strength and glass-forming ability of CoFeTaB bulk glassyalloy

Abstract

Co43Fe20Ta5.5B31.5 bulk glassy alloy has the best glass-forming ability (GFA) among the Co-basedglassy alloys, and the highest strength (the compressive true strengthσf = 5185 MPa) among all known bulk crystalline and glassy alloys. With the aim of synthesizingnew Co-based bulk glassy alloys with much higher strength and much largerGFA, we investigated the effect of Mo and Si additions on the enhancement ofσf and GFA in the Co–(Fe, Mo, Ta)–(B, Si) system. The small amount of2 at.% Mo added to the Co–Fe–Ta–B glassy alloy resulted in obtaining anultrahigh true fracture strength of 5545 MPa and high Young’s modulus(E) of 282 GPa. By further adding 1 and 2 at.% Si, Co–(Fe, Mo, Ta)–(B, Si) bulk glassyalloys were synthesized in the diameter range up to 3 mm, and they exhibitedσf of over4450 MPa and E of over 227 GPa. In addition, the ultrahigh-strength glassy alloys simultaneously exhibited excellentsoft magnetic properties, i.e., saturation magnetization of 0.32–0.35 T, low coercive force of0.7–1.1 A m−1, and high effectivepermeability of 3.9–4.77 × 104 at 1 kHz. The improvement of GFA andσf is interpreted to result from the enhanced atomic bonding nature by adding Mo and Si.